THE CONTINENTAL FLORA OF SOUTH SWEDEN 375 



Attention should be drawn in passing to the remarkable fact that Ledum 

 appears as a cliff-plant in the south-east of Central Europe (Drude 1902, p. 480). 



The distribution limit of Ledum towards the west is of great interest. In the 

 Scandinavian Peninsula it is distributed practically all over Sweden, while in 

 Norway it is found only in tlie extreme north (in Finnmarken and Tromso Amt to 

 Reisen) and very far to the south-east, with some few occurrences near the 

 Swedish border. In view of its distribution in the north of Scandinavia, Heintze 

 1909, and Paries 19 13 have maintained that Ledum ought to be regarded as a 

 species immigrating from the east. In South Sweden the species occurs far 

 more abundantly in the eastern and central parts than in the south-western part. 

 [A detailed investigation of its distribution is now being carried out by another 

 writer.] In the north of Germany Ledum has a westerly limit which shows a 

 great resemblance to the westerly limit of many steppe species (see Appendix I, 

 p. 414, and Graebner 1901, the map). 



What determines the limit of Ledum in the Baltic flora region it is difficult 

 to decide. It may be climatic factors, but also a competition with westerly 

 species, chiefly Erica tetralix. A detailed investigation of the mode of occur- 

 rence and distribution of the species might perhaps give an answer. 



Summary. 



The species treated in this chapter might, with regard to their distribution in 

 South Sweden, be divided into three groups. The first comprises species with 

 a distribution over practically the whole of South Sweden; and the distribution 

 corresponds more or less closely to the distribution of types of vegetation. To 

 this group belong the majority of the forest species here treated and, of the 

 others, Calla palustris and, though to a smaller degree. Ledum palustre. The 

 second group comprises species with only one or two or a somewhat larger 

 number of very much scattered occurrences. The distribution of these species 

 seems to correspond very slightly to the possibilities of occurrence in the region. 

 Under this group, above all, fall the marsh species and some of the species of 

 the flood-meadows. The third group consists of species which have a more or 

 less restricted distribution, a distribution that does not at all correspond to the 

 distribution of types of vegetation. This, however, comprises regions of a geo- 

 graphical character which are to some degree of a special nature, e. g. the ex- 

 treme south of Sweden, the south-east of Sweden, and can therefore be imagined 

 to correspond approximately to the occurrence-possibilities of the species in 

 South Sweden, e. g. Corydalis cava, Ulmus foliacea and laevis, Carex vulpina. 

 Ononis arvensis, and Inula britannica. 



